Question: $ { {4} \times \left[\begin{array}{rr}{1} & {3} \\ {1} & {2} \\ {1} & {3}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{4}\times{1} & {4}\times{3} \\ {4}\times{1} & {4}\times{2} \\ {4}\times{1} & {4}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{4} & {12} \\ {4} & {8} \\ {4} & {12}\end{array}\right]}$